Everything is just a matter of organization. The way we organize our thoughts, our fears, and our work helps us understand, perceive, and make decisions in the world around us.
There is no such thing as the perfect organization. There’s only a system that works for you or doesn’t work at all and needs change. But most people prefer to accept their own confusion as stupidity and ignorance rather than a disassembly of thinking systems. The brain is no different than a notepad and a shelf, it just needs to be sorted out so it can remember where it put things.
Smart people may actually have a bigger brain than you, but they also know how to leverage the brain’s hard disk space to create a critical system of folders that allows them to connect different pieces of information more quickly. They also excel at focusing, knowing when to use their brain's bandwidth at its maximum capacity.
You’re not stupid, not at all, but possibly mentally disorganized. The good news is that brain is malleable and can be cleaned up.